1. Field of the Invention
The present invention relates in general to capacitor characteristics measurement/packing apparatus, and, more particularly, to apparatus for measuring characteristics such as the capacitance of chip type capacitors and insulation resistance thereof and for packing them into tapes or cases.
2. Description of the Prior Art
Typically, capacitors are subjected before delivery or xe2x80x9cship-outxe2x80x9d to measurement of the electrostatic capacitance and insulation resistance (IR) thereof for selecting acceptable capacitors from among those under test, while screening out any defective ones based on the resultant measurement values thereof. This selection or screening process requires efficient handling of a great number of capacitors. To attain this object, certain characteristics measurement apparatus has been known which is disclosed in Published Unexamined Japanese Patent Application No. 4-254769, wherein the apparatus is designed to make use of a disk-shaped turn table having along its outer periphery multiple holder sections each of which holds a single capacitor at a time during intermittent rotation of the turntable for sequential effectuation of the measurement processes required.
Unfortunately, the prior known characteristics measurement apparatus of this type is associated with a problem: much time is required to complete the IR measurement. More specifically, since it is necessary in the prior art IR measurement scheme to measure a charge current under the condition that a capacitor is fully charged, approximately sixty (60) seconds of measurement time duration has been required for each IR measurement. For this reason extra time-consuming tasks have been necessary including reserving most of the turntable periphery for use as a charge region, and interrupting the operation of the turntable to complete a charging process in a certain time period, which results in a decrease in work efficiency. In addition, there is a need to put a predetermined number of acceptable capacitors into a storage member, such as a take-out vessel, and then take every capacitor out of the vessel by use of a parts feeder or the like in a one-by-one manner in order to supply them to an associative taping device or the like, which, in turn, leads to a significant decrease in the overall speed of work, measurement and packing operations, while simultaneously increasing the scale of facility and production costs.
It is therefore an object of the present invention to provide capacitor characteristics measurement/packing apparatus capable of improving the working efficiency while reducing facility size and cost, by letting characteristics measurement apparatus and packing apparatus cooperate with each other.
To attain the foregoing and other objects, the present invention is directed to a capacitor characteristics measuring and packing apparatus which includes transport means driven in a predefined direction and having holders provided at equal intervals for holding respective capacitors therein, supply means provided adjacent to the transport means for sending and supplying capacitors to the holders of the transport means, quality discriminating means provided on a movement locus at the holders of the transport means for applying a DC voltage to a capacitor held by one of the holders and discriminating the quality of the held capacitor from charge characteristics of the capacitor at an initial charge period, an acceptable product extraction section provided adjacent to the transport means for ejecting from the holder section of the transport means a capacitor determined to be acceptable at the quality discriminating means, a defective product ejection section provided adjacent to the transport means for ejecting from the holder section of the transport means a capacitor determined to be defective at the quality discriminating section and packing means disposed corresponding to the acceptable product extraction section for packing those acceptable capacitors.
Capacitors supplied to the holders of the transport means by the supply means pass through the quality discriminating means upon the driving of the transport means and the quality thereof is discriminated. As a method of discriminating the quality of the capacitor there may be a method in which a current value in a charge region at a dielectric polarization component of a capacitor and the quality of the capacitor is discriminated from this predicted value. Also, there may be a method in which a standard selection value charge characteristic of the dielectric polarization component of the capacitor is set beforehand and the quality of the capacitor is discriminated by comparing the actual measured current value characteristic of the dielectric polarization component of the capacitor and the standard selection value charge characteristic. Since a current value at a charge termination period is measured in the prior art, much time is required. According to the present invention, however, since a method for predicting a current value or a charge characteristic in an initial charge period is used, measurement can be performed in a significantly short period. The quality of the capacitor is discriminated by a predicted IR value or by comparing the actual measured current value characteristic and the standard selection value current characteristic. The capacitors determined as defective product are ejected from the defective product ejection section and the capacitors determined as acceptable product are supplied from the acceptable product extraction section to the packing means and packed in cases or tapes here.
As an IR prediction section for predicting the current value in a charge termination period by using the current value in an initial charge period of the dielectric polarization component, for example, a method may be used comprising the steps of: initial setting a current calculation formula using an equivalent circuit of the capacitor, modifying the current calculation formula using an equivalent circuit of the capacitor, modifying the current calculation formula by determining the capacitances C1, C2, . . . Cn and the resistances R1, R2, . . . Rn which are dielectric polarization component of the equivalent circuit so that the actual measured current value m(t) and the calculated current value j(t) determined by the current calculation formula coincide with each other, and determining the current value in the charge termination period by using the modified calculation formula. Further, a method may be used wherein the approximation formula of the charge current characteristic of the dielectric polarization component from the plural measured current values in the initial charge period of the dielectric polarization component of the capacitor is used.
When the quality of the capacitor is discriminated, it would be preferable to discriminate by using not only the IR prediction value but also the capacitance of the capacitor. In this case, the quality discriminating means includes a capacitance measurement section and the quality discriminating section discriminates the quality of the capacitor from the measured value at the capacitance measurement section and the predicted value at the IR prediction section.
When the quality is discriminated by using a standard selection value current characteristic, the standard selection value current characteristic is set, for example, in an intermediate region between acceptable products and defective products. As a result, the quality of the capacitor can be accurately discriminated by comparing the actual measured current value characteristic of the dielectric polarization component of the capacitor to be measured and the standard selection value charge characteristic. Since the quality is discriminated by continuous data of the dielectric polarization component, more accurate quality discrimination is possible than the prior art in which the quality is discriminated by point data.
As a quality discriminating means by comparing the actual measured current value characteristic and the standard selection value current characteristic, there may be a means wherein either one of the ratio, the difference, the difference of logarithmic values, or the ratio of logarithmic values between the actual measured current value m(t) of the capacitor and the standard selection value charge characteristic is defined as an evaluation function n(t), wherein said means includes a means for quadratic curve approximating this evaluation function and a means for discriminating the quality of the capacitor depending on whether the secondary coefficient of the quadratic curve approximation formula is negative or positive.
By using the method above, the quality discrimination can be performed accurately in a quite short period, that is, several tens of m seconds after the application of voltage. Further, by using a quadratic curve approximation, since the general tendency of the changes of the evaluation function n(t) can be attained, stable quality discrimination can be performed.
The transport means may be a turn table having holders for holding capacitors along the outer circular periphery at equal pitch intervals or an endless belt with holders for holding capacitors at equal pitch intervals. In the prior art, since much time was required for IR measurement, a large-sized turn table had to be used. However, according to the present invention, the measurement may be performed by using a small-sized turn table. Holders may be recessed portions for containing the capacitors or air attraction holes for attracting and holding the capacitors. When air attraction is performed, it is not necessary to provide recessed portions.
Further, the packing means may be taping means for housing an acceptable capacitor taken out of the acceptable product extraction section into a storage section of a base material tape, and for thereafter pasting a cover tape onto the base material tape. Also, the packing means may be case-packing means for string in a case a group of a predetermined number of acceptable capacitors as taken out of the acceptable product extraction section.